The classic colorful rotating puzzle Rubik’s Cube has been around for 50 years. It has not only endured, the cube has spawned innovative versions that are more challenging to solve than the original.

Japanese toymaker MegaHouse has made a replica that is hard to solve using only one’s hands. With each side measuring only five millimeters across, it is so tiny that a pair of tweezers is needed to rotate it. In contrast, the standard cube is 2.2 inches across each face.

Guinness World Records confirmed the micro-cube as the world’s smallest rotating puzzle cube in August, CNN reports.

Meanwhile, the micro Rubik’s Cube pales in comparison to the size of what scientists say lurk in showerheads and toothbrushes.

Erica Hartmann, an associate professor at Northwestern University’s McCormick School of Engineering in Evanston, Illinois, USA, and her team of researchers found many new viruses breeding in the warm and damp environments of one’s showerhead and toothbrush.

The findings reported in the journal Frontiers in Microbiomes were based on studies of samples of biofilms attached to the surface of 34 toothbrushes and 92 showerheads. More surprisingly, the viruses were not the kind that give one the common cold or flu, rather they were bacteriophages, the natural enemy of bacteria, according to CNN.

For every bacterium, there’s potentially tens or hundreds or even thousands of viruses that infect it, CNN quoted Hartmann as saying, with the viruses mutating very quickly.

She hypothesized that a bacterium in one’s mouth could transfer to one’s toothbrush, taking its viruses with it — and these could keep evolving on the toothbrush, the report says.

“And so it’s possible that there are viruses that are basically endemic to your toothbrush and are found nowhere else on earth,” Hartmann said, according to CNN.